FIG. 5 shows a prior art pattern defect inspection apparatus. In FIG. 5, the numeral 21 designates a light source, numeral 22 designates an iris for producing an irradiation section of the light emitted from the light source 21, and numeral 23 designates a collecting lens for collecting the light. Numeral 24a designates a stage on which a material to be inspected 24 is mounted, and numeral 25 designates an image sensor which receives the light which has transpared the material 24. Reference numeral 14 designates a stage driving circuit for driving the stage 24a. Reference numeral 13 designates a video memory and video signal operator for storing the video signal obtained by the image sensor 25 and for executing a predetermined operation to the obtained video signal. Reference numeral 15 designates an auxiliary memory device for storing inspection data. Reference numeral 11 designates a control operation apparatus for controlling devices 13, 14, and 15 to obtain pattern defect information corresponding to the material 24.
The device operates as follows:
Light is emitted from the light source 21, reformed by the iris 22 to produce an irradiation section collected by the collecting lens 23, and irradiated onto the material to be inspected 24. The light which has transpared the material 24 has a brightness and darkness pattern in accordance with the pattern of the material 24. This light pattern is irradiated onto the image sensor 25. Thus, a video signal which has the intensity in proportional with the intensity of the light on each picture element is obtained by the image sensor 25. This video signal is stored in the video memory 13. The stored video data is processed using filtering, smoothing, and binarization performed by the video signal operator 13. A pattern data for inspection read out from the auxiliary memory device 15, and is stored into a separate video memory. The values of these two video memories are compared with each other to determine the pattern defects of the material. Then the positions of the defects on the material are calculated by taking into consideration the stage position and communicated to an operator.
In the pattern defect inspection apparatus using such a construction, although the edge of the obtained pattern is likely to fade to about the extent of the light wavelength, the preciseness of the pattern defect inspection is enhanced by the fact that signal processing is used to the obtained video signal. However, recently such an optical method in the pattern defect inspection has reached its limitation in preciseness. The limitation has been reached where the pattern is miniaturized and the width of the pattern is in the submicron region.